linux-kernel - Re: [PATCH v4 00/14] forcealign for xfs

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Message-ID: <c702379b-3f37-448d-ac28-ec1e248a6c65@oracle.com>
Date: Mon, 23 Sep 2024 13:33:12 +0100
From: John Garry <john.g.garry@...cle.com>
To: Christoph Hellwig <hch@....de>
Cc: Dave Chinner <david@...morbit.com>,
        Ritesh Harjani
 <ritesh.list@...il.com>, chandan.babu@...cle.com,
        djwong@...nel.org, dchinner@...hat.com, viro@...iv.linux.org.uk,
        brauner@...nel.org, jack@...e.cz, linux-xfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        catherine.hoang@...cle.com, martin.petersen@...cle.com
Subject: Re: [PATCH v4 00/14] forcealign for xfs

On 23/09/2024 13:07, Christoph Hellwig wrote:
> On Mon, Sep 23, 2024 at 09:16:22AM +0100, John Garry wrote:
>> Outside the block allocator changes, most changes for forcealign are just
>> refactoring the RT big alloc unit checks. So - as you have said previously
>> - this so-called madness is already there. How can the sanity be improved?
> 
> As a first step by not making it worse, and that not only means not
> spreading the rtextent stuff further,

I assume that refactoring rtextent into "big alloc unit" is spreading 
(rtextent stuff), right? If so, what other solution? CoW?

> but more importantly not introducing
> additional complexities by requiring to be able to write over the
> written/unwritten boundaries created by either rtextentsize > 1 or
> the forcealign stuff if you actually want atomic writes.

The very original solution required a single mapping and in written 
state for atomic writes. Reverting to that would save a lot of hassle in 
the kernel. It just means that the user needs to manually pre-zero.

> 
>> To me, yes, there are so many "if (RT)" checks and special cases in the
>> code, which makes a maintenance headache.
> 
> Replacing them with a different condition doesn't really make that
> any better.

I am just saying that the rtextent stuff is not nice, but it is not 
going away. I suppose a tiny perk is that "big alloc unit" checks are 
better than "if (rt)" checks, as it makes the condition slightly more 
obvious.